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Mechanisms of factor VIIa‐catalyzed activation of factor VIII
Author(s) -
SOEDA T.,
NOGAMI K.,
MATSUMOTO T.,
OGIWARA K.,
SHIMA M.
Publication year - 2010
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2010.04042.x
Subject(s) - chemistry , thrombin , tissue factor , cleavage (geology) , coagulation , proteolysis , von willebrand factor , factor x , platelet activation , platelet , biochemistry , biophysics , enzyme , immunology , medicine , biology , paleontology , fracture (geology)
Summary. Background: Factor (F)VIIa, complexed with tissue factor (TF), is a primary trigger of blood coagulation, and has extremely restricted substrate specificity. The complex catalyzes limited proteolysis of FVIII, but these mechanisms are poorly understood. Objectives: In the present study, we investigated the precise mechanisms of FVIIa/TF‐catalyzed FVIII activation. Results: FVIII activity increased ∼4‐fold within 30 s in the presence of FVIIa/TF, and then decreased to initial levels within 20 min. FVIIa (0.1 n m ), at concentrations present physiologically in plasma, activated FVIII in the presence of TF, and this activation was more rapid than that induced by thrombin. The heavy chain (HCh) of FVIII was proteolyzed at Arg 740 and Arg 372 more rapidly by FVIIa/TF than by thrombin, consistent with the enhanced activation of FVIII. Cleavage at Arg 336 was evident at ∼1 min, whilst little cleavage of the light chain (LCh) was observed. Cleavage of the HCh by FVIIa/TF was governed by the presence of the LCh. FVIII bound to Glu‐Gly‐Arg‐active‐site‐modified FVIIa ( K d , ∼0.8 n m ) with a higher affinity for the HCh than for the LCh ( K d , 5.9 and 18.9 n m ). Binding to the A2 domain was particularly evident. Von Willebrand factor (VWF) modestly inhibited FVIIa/TF‐catalyzed FVIII activation, in keeping with the concept that VWF could moderate FVIIa/TF‐mediated reactions. Conclusions: The results demonstrated that this activation mechanism was distinct from those mediated by thrombin, and indicated that FVIIa/TF functions through a ‘priming’ mechanism for the activation of FVIII in the initiation phase of coagulation.